Conservator for oil-immersed transformers



May 24, 1965 SHlNJl NAKAZAWA ETAL CONSERVATOR FOR OIL-IMMERSED TRANSFORMERS Filed Jan. 28, 1964 2 Sheets-Sheet I sum WEEK]? TOHRU NHKRZHWH WWW Md Im/w,

WWW/'30 SHINJI NAKAZAWA ETAL 3,253,081

CONSERVATOR FOR OIL-IMMERSED TRANSFORMERS Filed Jan. 28, 1964 May 24, 1966 2 Sheets-Sheet 2 INVENTOR. SHINJI NHKHZHWH TDHRU NAKH lawn United States Patent 3,253,081 CONSERVATOR FOR OIL-IMMERSED TRANSFORMERS Shinji Nakazawa and Tohru Nakazawa, both of 1057 Hiratsuka 7-chome, Tokyo, Japan Filed Jan. 28, 1964, Ser. No. 340,703 Claims priority, application Japan, Aug. 19, 1963, 38/4 1,267; Oct. 14, 1963, 38/ 77,069 7 Claims. (Cl. 174-14) The present invention relates to improvements in a conservator for oil-immersed transformers.

Shinji Nakazawa, one of the present applicants, has invented previously a conservator for an oil immersed transformer, as described in the specifications of Japanese Patents No. 207,794 (patented in 1954) and 295,687 (patented in 1962). The invention described in the specification of said Japanese Patent No. 295,687 corresponds to that described in the specification of the United States Patent No. 3,067,277 or of British Patent No. 929,692.

The conservator described in the specification of said Japanese Patent No. 207,794 is, as described hereinafter, provided with an oil-proof, gas-tight and flexible bag, for example, of synthetic rubber, installed Within a conserva tor housing which communicates with the interior of the transformer tank, the neck of the bag floating on the oil level in the conservator housing being fixed to an upper portion of the conservator housing so that the interior of the bag communicates with ambient air. In this arrangement, the bag breathes according to the expansion or contraction of the transformer oil. Consequently, pressure rising in the bag will be avoided and the transformer oil may be isolated from ambient air.

According to the invention of Japanese Patent No. 295,687, an expansible metal cell filled with inert gas, for use on an oil-immersed transformer comprises a plurality of rectangular and triangular metal plates, the adjacent edges of said plates being so bonded with one another by means of a gas-tight and resilient seaming material as to constitute an expansible metal cell capable of folding in or out, and the interior of the cell communicating with the upper space within a conservator filled with inert gas, so that the cell expands or contracts in response to expansion or contraction in volume of the transformer oil in order to maintain a constant gas pressure.

According to the present invention, the conservator of the prior kinds comprises an oil-proof, gas-tight and expansible oil sealing cell (including the flexible bag and expansible metal cell in the aforementioned patents), a

' lower portion of said oil-proof, gas-tight and expansible oil sealing cell being rigidly attached to the bottom of a conservator housing so as to connect the interior of said oil sealing cell with that of a transformer tank through an oil-communicating fitting provided at a lower portion of said oil sealing cell. Thereby the interior of said "ice tate the operation of said expansible cell; especially, to effectively prevent ambient air or water from permeating through the structural material of the cell into the interior, in order to safeguard the insulation oil against deterioration; and to provide a conservator capable of being readily constructed.

The accompanying drawings illustrate prior conservators and two embodiments according tothe present invention. In the drawings,

FIG. 1 is a side view, with some parts shown in section, of an oil-immersed transformer provided with a prior conservator which comprises an oil-proof, gas-tight and flexible bag communicating with ambient air;

FIG. 2 is an enlarged view of the conservator shown in FIG. 1, with a part thereof shown in section;

FIG. 3 shows a side view, with some parts shown in section, of an oil-immersed transformer provided with another prior conservator which comprises an expansible cell made of metal plates;

FIG. 4 is a developed view of the metal plates used in the construction of the expansible cell shown in FIG. 3;

FIG. 5 represents the expansible cell shown in FIG. 4 as installed in the outer housing;

FIG. 6 is a side view of an oil-immersed transformer provided with one embodiment of a conservator according to the present invention;

FIG. 7 is an enlarged sectional view of the conservator shown in FIG. 6;

FIG. 8 shows a longitudinal section of the conservator shown in FIG. 7; and

FIG. 9 is a longitudinal section of another embodiment of the conservator according to the present invention.

In an example of the invention of Japanese Patent No. 207,749, which is depicted in FIG. 1 and FIG. 2 of the accompanying drawings, the oil-immersed transformer, designated as 10, is provided with a conservator 14, the housing of which communicates with the interior of the transformer 10 through a pipe 12 and contains partof the insulation oil of the transformer. A flexible bag 18 installed in the conservator housing floats on the insulating oil level and its neck is fixed to an upper portion of the conservator housing by means of a pipe 16 which connects the interior of the bag 18 with atmospheric air. The conservator housing is also provided with an evacuating pipe 22 having a valve for evacuating the air Within a space 20 above the oil level. In this arrangement, when the volume of the insulating oil changes owing to the variation in the output of the transformer or ambient temperature, air in the bag 18 enters or exits through the pipe 16, so that the bag breathes in response to expansion or contraction in volume of the transformer insulating oil.

In the aforementioned construction of the conservator,

however, ambient air or moisture contained in ambient oil-proof, gas-tight and expansible oil sealing cell will be filled with a portion of the oil in the transformer tank, The conservator housing contains separate oil, independent of the oil in the transformer tank, to a depth such that said oil-proof, gas-tight and expansible oil-sealing cell may be immersed below the level of said separate oil so as to balance the pressure in said oil-sealing cell with that outside of said cell. A space is kept above the level of said separate oil in the conservator housing when said cell is filled with the oil, and an air-communicating fitting, which connects the space above said separate oil with ambient air, is provided at an upper portion, for example a top plate, of the conservator housing.

The objects of the present invention are: to eliminate stresses acting on the expansible cell used to isolate the insulation oil from ambient air or other gases, and faciliair permeates into the transformer insulation oil through the bag 18 made of synthetic rubber or vinyl resin with resulting deterioration of the insulation oil. Furthermore, the bag is subject to stresses owing to negative pressure occurring around the bag and forced to stick to the inner side of the conservator housing. As a result, the bag becomes wrinkled and decreases its volume. Thus it is difficult to expect stable operation of the conservator.

FIG. 3 shows a transformer having a nitrogen-sealed conservator, wherein the oil-immersed transformer 11 is provided with a conservator 17 mounted on its top. The lower inner portion of the conservator 17 communicates with the interior of the transformer through a pipe 13 and constitutes an oil reservoir containing part of the insulation oil of the transformer, and the upper portion 15 is filled with dry nitrogen gas acting as sealing gas. In a housing 19 is an expansible cell 21 made with. a plurality of metal plates, the adjacent edges of which are bonded with one another by means of synthetic rubber, vinyl resin or any other plastic material, or flexible metal sheet to provide a cell capable of folding in or out. The cell 21 is also filled with dry nitrogen gas and communicates with the upper portion 15 of the conservator 17 through a pipe 31. When the insulation oil in the transformer 11 expands or contracts, the gas in the conservator 17 is forced into or drawn out of the cell 21 to cause expansion or contraction of the latter, so that the pressure of the sealing gas may be kept constant.

According to Japanese Patent No. 295,687, as shown in FIG. 4, the cell consists of two rectangular metal plates 23 23 four rectangular metal plates 25 25 which are equal in length to the metal plates 23 23 and in width to one half or less than one half of said metal plates 23 23 four equilateral triangular metal plates 27 27 whose bases are equal to the width of said metal plates 23 23 and eight triangular metal plates 29 29 which are in area a little less than one half of said equilateral triangular metal plates 27 27 The metal plates are arranged in the manner illustrated in FIG. 4, and adjoining edges of the metal plates are bonded with one another by means of a resilient, gastight and durable seaming material such as synthetic rubber, vinyl resin or any other similar material, or elastic,

. thin corrugated metal sheet, so that an expansible metal cell 21, capable of folding in or out in response to expansion or contraction in volume of the transformer insulation oil, will result.

FIG. 3 and FIG. show the aforementioned cell 21 installed within the housing 19. The cell 21 communicates with the gas-containing space 15 in the conservator 17 through a gas-communicating pipe 31, so that the cell 21 will be filled with same inert gas as in the space 15. In this arrangement, a portion of the cell 21, for example the front plate, is rigidly attached to the inner side of the housing 19, and wheels 33 and guiding rails 35 are provided to facilitate expansion or contraction of the cell, if desired. Thus, the cell 21 varies its volume in response to expansion or contraction in volumeof the transformer insulation oil without bringing about variation of sealing gas pressure in the conservator.

Since, according to the application of the cited invention, the major parts of the expansible cell are made with metal plates, the amount of air and oxygen or water contained in ambient air permeating into the cell interior is extremely less than that in the construction according to the aforementioned Japanese Patent No. 207,794. How ever, this arrangement requires the use of nitrogen gas as Well as considerable additional space and expenditure for the cell containing gas and piping thereof.

FIGS. 6, 7 and 8 illustrate a first embodiment of the present invention, wherein the expansible cell made with metal plates according to the prior invention is used as an oil-sealing cell.

The oil-immersed transformer, shown in FIG. 6, is provided with a conservator 41 according to the present invention mounted on the top of a transformer tank 40.

The conservator 41 is shown in detail in FIGS. 7 and 8.

In the housing 42 of the conservator, an oil-sealing cell 43 having same construction as that of the metal expansible cell 21 described in FIGS. 3 and 4 is installed. The metal plate forming a major surface of the cell 43 (the plate 23 or 23 in FIG. 4) is fixed to the bottom of the conservator housing 42 by means of a resilient piece 44 made of synthetic rubber or any other similar material and attached to said metal plate and a fastening piece thereof. The fixing piece 44 is provided with a bore 45 for passing the insulation oil therethrough. The interior of the cell 43 communicates, as shown in FIG. 6, with that of the transformer tank 40- by means of a communieating pipe 46 and is filled with part of the insulation oil in the tank 40. The conservator housing 42 contains pressure-balancing oil 47, independent of the oil within the transformer tank 40 and the cell 43, to the depth that the upper surface of the cell 43 will be kept below the level of the oil 47 at expansion or contraction in volume of the cell. A space 48 remaining above the level of the oil 47 within the housing 42 communicates with ambient air through a pipe 50 mounted on the upper plate 49 of the housing 42. Further, at the bottom of the housing 42 a well 51 having a drain cock 52 is provided, so that water entering together with air into the housing 42 through the pipe 50 and staying on the bottom of the housing, is collected in the Well 51 and drained therefrom. At an upper portion of the cell 43 a self-sealing vent opening 53, which closes in an air-tight manner, is provided. Accordingly, when part of the insulation oil rises into the cell 43 and fills it, air within the cell 43 may escape through opening 53. In operation of the oil-immersed transformer the expansible oil-sealing cell 43 immersed in the pressure-balancing oil 47 expands or contracts in response to variation in volume of the transformer insulation oil, causing the space 48 to carry out breathing action according to said variation in volume of the transformer insulation oil.

Since the exterior as well'as the interior of the expansible oil-sealing cell 43 is isolated from ambient air, and the cell operates in the pressure-balancing oil 47 independent of the transformer insulation oil, pressures at the outside and the inside of the cell will be balanced, with re sult that no stresses are applied on any parts of the cell. Further, ambient air or water contained in said air getting into the oil 47 scarcely permeates into the cell 43, and the water staying on the bottom of the conservator is collected in the well 51. Namely, according to the present invention, the expansible oil-sealing cell 43 immersed in the pressure-balancing oil is free from stresses applied thereon, with resulting in smooth operation thereof, and the transformer insulation oil is prevented from mixing with ambient air and water contained in said air by means of the pressure-balancing oil and the expansible oil-sealing cell, so that the conservator carries out the desired operation for a long time.

Some of the metal plates constituting the cell 43 may be substituted with plates of "same size made of synthetic rubber or vinyl resin.

FIG. 9 shows a second embodiment of the present invention, wherein a bag made of synthetic rubber, vinyl resin or any other plastic material, as described in the aforementioned Japanese Patent No. 207,794, is used as the oil-sealing cell. The construction in this embodiment is similar to that in the first embodiment with the excep tion that the expansible bag 54, for example made of synthetic rubber, is used in place of the oil-sealing cell 43, so that like parts are designated with like reference characters. The manner of operation in the second embodiment is also similar to that in the first embodiment. The bag 54 made of synthetic rubber or any other plastic material is a little inferior to the oil-sealing cell made with metal plates with respect to greater permeability of air or water, but superior in simplicity of construction and easiness of manufacturing and mounting. The second embodiment, however, has the advantage that pressures at the outside and the inside of the bag will balance with the result that no stresses are applied on any parts of the bag so that the amount of air or water permeating into the bag is extremely small, as compared with the conventional construction. As mentioned above, in the construction according to the invention of Japanese Patent No. 207,794, negative pressure occurs around the bag within the conservator housing in proportion to the height of the bag and causes the upper portion of the bag to become wrinkled during operation. As a result, the usable height of the conservator is restricted. In case a weak point arises on the bag under stress owing to negative pressure, the weak point spreads gradually, so that ambient air will get into the bag and the oil will permeate out of the bag. On the contrary, the second embodiment of the present invention has the advantages as follows:

(1) Pressures at the outside and the inside of the bag will be balanced, so that no stresses are applied on any parts of the bag,

(2) The bag operates smoothly without sticking to the ceiling of the conservator housing,

(3) The useable volume in the conservator increases, and

(4) The amount of air or water permeating into the bag becomes extremely small.

Having thus described the invention, what is claimed as new and desired to be secured by Letters Patent, is:

1. A conservator for oil immersed transformers comprising, in combination, a housing including an opening to atmosphere in an upper wall; an oil-proof, gas-tight and expansible oil sealing cell within said housing and secured to a bottom wall thereof; means extending through said bottom wall in sealed relation therewith and connecting the interior of said cell to the oil tank on the transformer containing the transformer insulation oil, whereby said cell is at least partially filled with transformer insulation oil; and a substantially constant volume supply of pressure balancing oil, independent of the tankcontained transformer insulation oil, in said housing to a depth suflicient to completely immerse said cell in the expanded condition of the latter while leaving an air space in said housing above the surface of said supply of pressure balancing oil and communicating with said opening; whereby said cell is completely sealed from air and the internal and external oil pressures thereon are substantially balanced at all times.

2. A conservator for oil immersed transformers, as claimed in claim 1, including a well on said bottom wall communicating with the interior of said housing; and a water drain cock communicating with said well to drain water, accumulating on the interior surface of said bottom wall, from said housing.

3. A conservator for oil immersed transformers, as claimed in claim 1, wherein said cell is formed by two rectangular metal plates of substantially equal size, four rectangular metal plates having a length substantially equal to that of said two rectangular metal plates and a width equal to less than one half of the width of said two rectangular metal plates, four equilateral triangular metal plates having a base width equal to the width of said two rectangular metal plates, and eight triangular metal plates having an area slightly less than one half that of said four triangular metal plates; and resilient, gas-tight and oilproof seaming material bonding adjoining edges of said metal plates to define said cell.

4. A conservator for foil immersed transformers, as claimed in claim 1, wherein said cell comprises an expansible bag of synthetic rubber having a bottom opening communicating with said means extending through said bottom wall and is secured to said bottom wall around the periphery of said bottom opening.

5. A conservator for oil immersed transformers, as claimed in claim 4, wherein said bag is made of vinyl resin.

6. A conservator for oil immersed transformers, as claimed in claim 3, wherein some of the metal plates consituting said cells are substituted by plates of plastic material.

7. A conservator for oil immersed transformers, as claimed in claim 3, wherein some of the metal plates constituting said cells are substituted by plates of synthetic ROBERT K. SCHAEFER, Primary Examiner.

JOHN F. BURNS, Examiner.

I. F. RUGGIERO, Assistant Examiner. 

1. A CONVERSATOR FOR OIL IMMERSED TRANSFORMERS COMPRISING, IN COMBINATION, A HOUSING INCLUDING AN OPENING TO ATMOSPHERE IN AN UPPER WALL; AN OIL-PROOF, GAS-TIGHT AND EXPANSIBLE OIL SEALING CELL WITHIN SAID HOUSING AND SECURED TO A BOTTOM WALL THEREOF; MEANS EXTENDING THROUGH SAID BOTTOM WALL IN SEALED RELATION THEREWITH AND CONNECTING THE INTERIOR OF SAID CELL TO THE OIL TANK ON THE TRANSFORMER CONTAINING THE TRANSFORMER INSULATION OIL, WHEREBY SAID CELL IS AT LEAST PARTIALLY FILLED WITH TRANSFORMER INSULATION OIL; AND A SUBSTANTIALLY CONSTANT VOLUME SUPPLY OF PRESSURE BALANCING OIL, INDEPENDENT OF THE TANKCONTAINED TRANSFORMER INSULATION OIL, IN SAID HOUSING TO A DEPTH SUFFICIENT TO COMPLETELY IMMERSE SAID CELL IN THE EXPANDED CONDITION OF THE LATTER WHILE LEAVING AN AIR SPACE IN SAID HOUSING ABOVE THE SURFACE OF SAID SUPPLY OF PRESSURE BALANCING OIL AND COMMUNICATING WITH SAID OPENING; WHEREBY SAID CELL IS COMPLETELY SEALED FROM AIR AND THE INTERNAL AND EXTERMAL OIL PRESSURES THEREON ARE SUBSTANTIALLY BALANCED AT ALL TIMES. 